In the well-known process of electrostatography or xerography, electrostatic latent images are created on a charge-retentive surface, either by direct exposure of a hard-copy original image or by digital means in response to image data. The electrostatic latent image is "developed" by general application of dry marking particles thereto. Typically, in such a development step, the marking particles are caused to adhere only to those areas on the latent image which are charged in a particular way. For example, depending on a specific design, the marking particles can be caused to adhere to relatively charged or discharged areas on the charge-retentive surface.
Many techniques for carrying out this development step are known in the art. The dry marking material which is used to develop the latent image is generally referred to as "toner." A number of development techniques require that toner particles be evenly mixed with a quantity of "carrier." Generally speaking, toner plus carrier equals "developer." Typically, toner particles are extremely fine, and responsive to electric fields; carrier particles, in contrast, are relatively large and respond to magnetic fields. In a "magnetic brush" development system, the developer is exposed to relatively strong magnetic fields, causing the carrier particles to form brush-like strands, much in the manner of iron filings exposed to a magnetic field. The toner particles, in turn, are triboelectrically adhered to the carrier particles in the strands. What is thus formed is a brush of magnetic particles with toner particles adhering to the strands of the brush. This brush can be brought in contact with the latent image, and under certain conditions the toner particles will separate from the carrier particles and adhere as necessary to the charge-retentive surface.
In commercially-available printers and copiers (as used in the specification and claims herein, a copier shall be considered a type of printer), it is well known that any individual printer periodically requires replenishment of its supply of developer or other marking material. It is typically desirable that such replenishment of a developer supply be performed by an end user, so that a service call by trained personnel is not necessary. Replenishment of developer, however, may present any number of inconveniences to a user. Toner material is typically in the form of a very fine powder which adheres easily to any surface, such as skin, which it may contact. Further, airborne toner particles can easily be inhaled by a user.
In order to overcome the inconveniences of manually replenishing a developer supply, it is typical to provide developer material in replacement cartridges, which can be readily "snapped in" to a printer or copier with minimal exposure of free toner particles to the outside. Co-pending U.S. Pat. application Ser. No. 08/254,204, assigned to the assignee hereof, generally discloses a developer supply replacement cartridge, which may be purchased at retail and installed in a copier or printer by a relatively unskilled end-user. The particular assembly disclosed in the application comprises two coupled containers, one intended to retain a supply of fresh developer material, and the other adapted to accept waste developer material from a dispenser forming part of the copier.
It is one object of the present invention to provide a supply cartridge for dispensing marking material in a printing apparatus such as a copier, which may be readily installed with minimal inconvenience by an end-user, and which is also of a low-cost design.